Sadly, I'm not sure if you will get anything larger than a group 51 (same physical size as your stock battery) in there... the space is pretty tight. Best thing to do would be to take out the battery and get a good look at the amount of space in there.
In my 04 Civic, it came with a group 51, that I thought was as big as I was going to get, but I took the battery out, and lo and behold, the tray was big enough for a group 34. Dropped one in and it fit like a glove. But like I said, I'm not sure if yours will work out the same way, it is VERY tight from what I remember seeing.